The invention relates to a method of internally coating a tube consisting of an electrically insulating material the coating is produced by reactive deposition from a gas mixture which is passed through the tube. The deposition is activated by a plasma which is reciprocally moved along the tube.
The invention also relates to an arrangement for internally coating a tube by means of a reactive deposition from a gas mixture which is passed through the tube. The arrangement comprises a gas supply system and means for producing a plasma in the gas phase in the tube and moving the plasma forward and backward through the tube.
Methods and arrangements of this type are known per se from, for example, U.S. Pat. No. 4,145,456 and United Kingdom Patent No. 1,578,826. According to the U.S. patent, high-frequency energy can be coupled into the tube by means of a cavity resonator. The coupling can be inductive or capacitive. The United Kingdom patent describes an inductive coupling via a coil. In both patents an additional heating of the tube is described. For that purpose an oven is employed in the U.S. patent. The United Kingdom patent describes the possibility of using the plasma to heat the tube. However, the use of an additional heat source to consolidate the deposited particles is not excluded and may be used in practice, as is described in later publications.